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Formation of niobium hydride precipitates in superconducting qubits

Zuhawn Sung1,*,†, Daniel Bafia1,*, Arely Cano2, Akshay Murthy1, Jaeyel Lee1, Matthew J Reagor3, Juan Rubio-Zuazo4,5, Anna Grassellino1, and Alexander Romanenko1

  • *These authors contributed equally to this work.
  • †Contact author: zsung@fnal.gov
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Phys. Rev. Materials 10, 016201 – Published 6 January, 2026

DOI: https://doi.org/10.1103/mgnw-kjps

Abstract

We report evidence for the formation of niobium hydride phase within niobium films on silicon substrates in superconducting qubits fabricated at Rigetti Computing. For this study, we combined complementary techniques—including room-temperature and cryogenic atomic force microscopy (AFM), synchrotron x-ray diffraction, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS)—to directly reveal the existence of niobium hydride precipitates on the surface of superconducting qubits. Upon cryogenic cooling, we observed variation in the size and morphology of the hydrides, ranging from small (∼5 nm) irregular shapes to large (∼10–100 nm) domains within the Nb grains, which were fully converted to niobium hydrides. Since niobium hydrides are nonsuperconducting and can easily change in size and location upon different cooldowns to cryogenic temperature, our finding highlights a previously unknown source of decoherence in superconducting qubits. This contributes to quasiparticle losses, offering a potential explanation for changes in qubit performance upon cooldowns. Finally, by leveraging the RF performance of a 3D bulk Nb resonator, we quantify RF dissipation in a superconducting qubit caused by hydrogen concentration variation, and propose a practical engineering pathway to mitigate the formation of Nb hydrides for superconducting qubit applications.

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Phys. Rev. Materials 10, 016201– Published 6 January, 2026
  • Received 18 August 2025
  • Accepted 19 November 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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